In modern magnetic data storage systems, actual recording of data is invariably done by a conventional magnetic transducer which converts an electrical signal into changing magnetic flux patterns at the flux gap of the transducer and adjacent a medium in which intricate magnetic patterns may be created. The changing magnetic flux patterns change the local magnetic state of the medium into a pattern in the medium which persists until overwritten. The pattern in the medium can be sensed or read by a variety of devices to create an electrical signal representative of the pattern in the medium and from which the original data can be recreated.
Photolithographic processes can be used to form such transducers, and those so formed are referred to as thin film transducers. Such transducers are built up through deposition layer by layer in great numbers simultaneously on a wafer which is then cut into individual carriers, each having one or two transducers. Each individual carrier then has a bearing surface along which the medium moves, and which is created by the cutting step. These transducers have at least one deposited pole of preselected width projecting toward and approximately flush with the bearing surface of the transducer. The pole defines a flux gap across which is formed the magnetic field for writing the magnetic pattern in the medium. A deposited winding encircling the pole carries write current for generating the write flux across the flux gap. If only a single pole is deposited for a transducer, then the carrier is formed of a magnetic ferrite and forms the other pole. Of course, it is possible to deposit two or more poles, and the flux gap for writing is then formed between them. In this case, the carrier may be formed from magnetic or non-magnetic materials depending on the configuration of the assembly.
One type of sensor for reading data encoded in previously written magnetic data patterns on the medium is a so-called magnetoresistive flux sensing element underlying the deposited pole. Such an element has the special characteristic of electrical resistance which is a function of the impressed magnetism to which such a sensor is exposed. The magnetoresistive sensing element has advantages and disadvantages for this application. One of the disadvantages is that the sensor must be carefully constructed so that it comprises a single domain in the area where the medium's magnetic pattern is sensed, thereby avoiding the Barkhausen noise which is otherwise generated. The Barkhausen noise problem requires careful design of these sensors to allow their proper functioning to sense magnetic patterns. To prevent the breakup of these sensors into a plurality of magnetic domains, among other things it is known to be necessary for the sensing element to physically have relatively straight edges and sides with no sharp angles since these can induce the element to break up into domains. These problems are considered in various discussions of magnetoresistive elements, among these being "Characteristic Length of Domain Structure and Its Effect on the Coercive Force of Ferromagnetic Materials", E. J. Ozimek, J.A.P. 57(12), June 15, 1985, p. 5406 and "Fabrication and Wafer Testing of Barber Pole and Exchange-Biased Narrow Track MR Sensors", IEEE Transactions on Magnetics, Vol. Mag 18, November 1982, pp. 1149-1151.
It is important that the sensor be located as close as possible to the medium and the magnetic patterns in it since these are relatively weak and their field drops off quickly with distance. Because of the single domain requirement and because of the way in which these composite transducers are manufactured, it is preferred that the sensing element be recessed slightly from the edge of the carrier on which the sensor and transducer are mounted. Recessing is needed to permit the write transducer flux gap to be configured to a particular range of dimensions, say by a lapping process, and if the sensing element is not sufficiently recessed, the sensing element can be scratched by the lapping process. These scratches may induce the sensor to break up into domains. These considerations require that the sensing element be accurately positioned on the support so that on the one hand the sensing element is close enough to accurately create the electrical signal during readback, and on the other hand not so close to the edge of the support that it is recessed insufficiently.
Another problem if the sensor is located too close to the edge of the carrier is that adjacent data tracks in the medium will be sensed by the sensor, and this cross talk will reduce the accuracy with which the sensor can reproduce the magnetic pattern in the selected track. By recessing the sensor slightly, the pole(s) serve as a flux path in conducting flux from the medium and the desired track therein to the sensor, at least partly to the exclusion of cross talk from adjacent tracks. Recessing thus alleviates the cross talk problem, but reduces the signal strength and makes the sensor more vulnerable to other noise sources.